But, if it's like a circle or a half circle, or things like that, then even if a problem doesn't tell you to do it in polar coordinates you might want to seriously consider it.
但是如果它是一个圆或者半圆，或者是类似的，即使题目没有提示你在极坐标里做，你也应该认真考虑一下。
2
Now we have a motion-tracking function that is run for every frame of video that comes in. Let's retrieve the coordinates and draw a blue circle where there is motion.
现在有了一个运动跟踪函数，对于视频的每一帧都会运行它。
3
Each half-circle is offset by computed x and y coordinates in order to ensure that they are concentric.